Liquid coolant for machining operations is being used in many manufacturing shops. Often, the coolant solution is a synthetic oil dissolved in water. The liquid coolant absorbs the heat generated by the friction which occurs between a carbide tool bit and the metal piece that is being machined. The coolant also serves to remove the metal cuttings (fines) from the surface of the metal piece during machining. If the metal fines are not removed from the machined part, clean, sharp shapes of exact dimensions will not be obtained. Further, the metal piece being machined is generally an alloy. Depending on the composition of the alloy, additional undesirable metal fines or particles can build-up or dissolve in the coolant solution. As a result, the dissolved metal and undissolved metal particles may reach toxic levels in the coolant solution. In addition, cutting oils from the machined parts accumulate in the coolant and should be removed. Thus, the life of any machining coolant depends on the concentrations of metal particulate, soluble metal, and cutting oils. Presently, if any of these concentrations appear excessive to the operator, the coolant is replaced. The spent coolant is collected and disposed of as waste. The coolant waste classification depends on what substances, such as the dissolved and undissolved metal, have contaminated the coolant.
As an example, a machining coolant is used in shaping lead-alloyed parts at a manufacturing plant. Approximately 4000 gallons per month of coolant are being used. The coolant is produced by mixing 5% by weight of synthetic oil with water. The synthetic oil is water soluble. When the coolant comes in contact with the lead alloys, the coolant becomes contaminated with lead. If the lead content of the coolant exceeds 5 ppm, it is considered hazardous waste and must be manifested and disposed of as a hazardous waste. The cost of disposal and the cost of the coolant replacement are high. For instance, about 2000 gallons of coolant are disposed of as hazardous waste every other week at a cost of $0.40/gallon. The cost of transportation of the spent coolant is $800/load. The cost of the fresh replacement coolant is $10/gal. The total cost of disposal is almost $70,000 per year. This cost does not include periodic chemical analysis, which is required for disposal, labor, and waste site storage.
Significant cost savings would result if the coolant solutions are treated to remove hazardous lead metal components and oil so as to regenerate the coolant solution for further use. There is a need for a new low cost and effective treatment process which removes both particulate and dissolved lead and accumulated oil from machining coolant solutions that would dramatically reduce both disposal and replacement cost of the coolant. There is also a need for a process that significantly prolongs the life of the coolant by continuously withdrawing a portion of solution, removing metal contaminants and oil from the solution and recycling the clean treated coolant to the coolant reservoir, thereby regenerating the coolant solution for further use in a manufacturing environment.